Question 1
A shock wave that is normal to the upstream flow is a rare case.
A. False
B. True
View Answer
Answer: Option A
Explanation:
The normal shock wave, i.e. the one normal to the upstream flow, seems rare. But actually, it is a very frequent case of shock waves and occurs at many times in different cases.
Question 2
For a calorically perfect gas, the ratio of stagnation to static temperature depends upon_______
A. γ
B. γ , M
C. M
D. R, M
View Answer
Question 3
For a non-perfect gas, if we double the pressure while keeping the temperature same, the speed of sound remains the same.
A. False
B. True
View Answer
Answer: Option A
Explanation:
For a non-perfect gas, the speed of sound is a pressure of temperature and pressure (or density). And hence, by changing the pressure, while keeping the temperature constant, speed of sound changes.
Question 4
For a perfect gas, if we half the density, keeping the temperature same the speed of sound changes. This is due to the change in pressure.
A. True
B. False
View Answer
Answer: Option B
Explanation:
The given statement is false. For a perfect gas, the speed of sound is a pressure of temperature only. And hence, by changing pressure or density but keeping the temperature same, speed of sound will not change.
Question 5
Mach number is a measure of the directed motion of the gas compared with the random thermal motion of the molecules.
A. False
B. True
View Answer
Answer: Option B
Explanation:
This comes from the physical meaning of the Mach number. When we take the ratios of per unit mass kinetic energy to the potential energy of the fluid particle moving along a streamline, it comes proportional to the square of the Mach number. Thus, this is true.
Question 6
Select the incorrect statement for the properties concerned with a flow.
A. a* and a0 are constant at a point
B. a* and a0 are constant along the streamline for an adiabatic, inviscid, steady flow
C. a* and a0 are constant along the entire flow for an adiabatic, inviscid, steady flow
D. a* and a0 are related but not equal
View Answer
Answer: Option C
Explanation:
a* and a0 are the defined properties of the flow, constant at a point. They are related to each other but not same. For an adiabatic, inviscid, steady flow they are constant along the streamline. And if all the streamlines are coming from same uniform free-stream, they are constant along the entire flow.
Question 7
Select the incorrect statement out of the following.
A. limτs→0 is the case of an incompressible flow
B. Speed of sound in incompressible medium is zero
C. Mach number for finite velocity object, in incompressible flow is zero
D. Incompressible flow is theoretically zero-Mach number flows
View Answer
Answer: Option B
Explanation:
Incompressible flow is the limiting case of isentropic compressibility being zero. This gives an infinite speed of sound and a zero Mach number in that medium. Thus, theoretically, zero-Mach number flows are incompressible.
Question 8
The characteristic Mach number and Mach number are related. Which of these is not correct?
A. M=1, M*=1
B. M<1, M*<1
C. M<1, M*<1
D. M→∞, M*→0
View Answer
Answer: Option D
Explanation:
The characteristic Mach number and the Mach number behave almost in a similar pattern. The only difference if when the Mach number tends to infinity, the characteristic Mach number tends to a finite value. This finite value depends only on gamma is never zero.
Question 9
The characteristic Mach number is constant for a given value of temperature and gamma.
A. False
B. True
View Answer
Answer: Option A
Explanation:
The defined M* or the characteristic Mach number depends upon the Mach number, for any given gamma. It changes if the Mach number is changed, which changes by changing the flow speed at any temperature. Hence, the given statement is false.
Question 10
The correct statement for a point where the speed of sound is a, is_______
A. a* is the stagnation speed of sound
B. a* is the maximum speed of sound
C. a0 is the characteristic speed of sound
D. a0 is the stagnation speed of sound
View Answer
Answer: Option D
Explanation:
For a point in the flow, where the speed of sound is a, a0 is the stagnation speed of sound associated with that point. While a* is the sonic characteristic value associated with that same point. None of these is the maximum speed of sound in the flow.
Question 11
The definitions of P0 and ρ0 involve______
A. Isothermal compression
B. Isentropic compression
C. Adiabatic compression
D. Any process gives the same value
View Answer
Answer: Option B
Explanation:
The defined properties of the flow P0 and ρ0 involve isentropic compression, which is adiabatic and reversible both. These properties are the values of the flow parameters when the flow is isentropically compressed to zero velocity, at a point with properties P and ρ.
Question 12
The most important quantity that dominates the physical properties of compressible flow is _______
A. Speed of sound
B. Speed of light
C. Density of medium of propagation
D. Distance of propagation
View Answer
Answer: Option A
Explanation:
The speed of sound is the quantity that dominates the physical properties of compressible flow. Speed of light is not important in compressible flow problems. Density of medium and distance of propagation are secondary quantities.
Question 13
The speed of sound in any medium is a function of_____
A. P, ρ
B. P, T
C. T only
D. T, ρ
View Answer
Question 14
Which is not the correct reason for sound of speed being higher in helium than in air at the same temperature?
A. γ for helium is higher than air
B. Gas constant is same for both
C. Helium is lighter than air
D. R for helium is much larger than for air
View Answer
Answer: Option B
Explanation:
The sound of speed depends on gamma, T and the gas constant R for the respective gas. In case of helium and air, the gamma for helium is higher than air. Also, helium is lighter than air thus, R for helium being higher. This gives, at the same temperature, speed of sound more in helium than air.
Question 15
Which is not true for continuity equation of normal shock?
A. ρ1u1A1=ρ2u2A2
B. ρ1u1=ρ2u2
C. Steady flow
D. No viscosity
View Answer
Answer: Option B
Explanation:
The continuity equation of the normal shock equation is derived from the continuity equation of mass and is given as ρ1u1A1=ρ2u2A2. If the area of the control volume is same on both sides, it becomes ρ1u1=ρ2u2. The flow is steady and without viscosity.
Question 16
Which of these is incorrect for the normal shock wave analysis?
A. No viscous effects or body forces
B. Adiabatic flow
C. Differential form of conservation equations used
D. Steady flow
View Answer
Answer: Option C
Explanation:
The normal shock wave analysis uses the control volume approach. The integral form of conservation equations are applied to the control volume. The flow is steady, adiabatic, without viscous effects and zero body forces.